RE: [Elecraft] Multimeter Altitude Limits
Hi Jim; I understand arcing at standard Temp. and pressure. I thought that the reduction of media would produce an increase of voltage Vs. distance (vacuum relays and Caps.) I'm missing something here. pete kn6bi -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Thursday, August 03, 2006 5:20 PM To: Elecraft@mailman.qth.net Subject: Re: [Elecraft] Multimeter Altitude Limits In our high altitude ballooning program at LSU (120,000 feet) it's necessary to be very careful about sharp edges and corners in circuits of even modest voltages. Vacuum chamber testing is an essential part of the payload development. Our student payload had a Geiger-Muller tube, and that's a couple hundred volts, so they had to be sure to test in the chamber. Interestingly... 6500 ft is 1981 meters, so I speculate a conversation like.. Pointy Haired Boss: We need an altitude limit because of HV arcing, what do think it should be? Alice: Oh, couple thousand meters or so should be safe enough. Pointy Haired Boss: OK, tell marketing. Alice: Fine, but remember we're selling it in the USA. Pointy Haired Boss: Not to worry, ad copy writers will take care of conversion. I recall a wireless device whose range was specified on the package to be up to 328 feet. Amazing how they knew it would work at 327 but not at 329. Of course what was meant was that the range was about 100 meters. :^)) 73 Jim N5IB ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com __ NOD32 1.1691 (20060803) Information __ This message was checked by NOD32 antivirus system. http://www.eset.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Multimeter Altitude Limits
On Fri, 4 Aug 2006 07:58:37 -0700 Peter writes: Hi Jim; I understand arcing at standard Temp. and pressure. I thought that the reduction of media would produce an increase of voltage Vs. distance (vacuum relays and Caps.) Air is a dielectric. While its dielectric *constant* is almost identical to vaccum, its dielectric *strength* (volts per distance) decreases with density (pressure) until you get into some really hard vacuum situations. See http://www.isi-seal.com/searchs/doc/DielectricStrength.htm for a chart. For air at STP it's about 3000 volts per millimeter In interpreting that chart, remember that standard atmospheric pressure is 760 torr, and at 2000 meters altitude (the notorious 6500 ft) the pressure is about 600 torr. Pressure and density aren't linearly related because of the temperature drop as you go up, but its a decent approximation for the first couple thousand meters or so. By the time you reach 300 torr, at about 7500 meters, the dielctric strength of air is degraded by about a factor of 2, and by 30,000 meters (10 torr) it's degraded by about 90%. We routinely fly our balloons above 38,000 meters. See http://weather.uwyo.edu/cgi-bin/sounding?region=naconfTYPE=TEXT%3ALISTYEAR=2006MONTH=08FROM=0412TO=0412STNM=72240 for a representative chart of pressure, altitude, and other meteorological parameters. The vacuum relays and caps incorporate some pretty hard vacuum, I'd surmise. Pretty bitter pill to swallow... paying premium bucks for a better grade of nothing :^)) So, if your working around higher voltages than most of our QRP gear, I guess it's best not to inhale :^)) 73 Jim N5IB ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Multimeter Altitude Limits
Correct. Pressure and density are not the same thing. But if we are talking about arcing, should we be more concerned with pressure altitude, or density altitude? A higher than standard temperature can make a huge difference in the two. As an old pilot, I had to ask! Dan Allen KB4ZVM K-2 S/N 1757 Air is a dielectric. While its dielectric *constant* is almost identical to vaccum, its dielectric *strength* (volts per distance) decreases with density (pressure) until you get into some really hard vacuum situations. See http://www.isi-seal.com/searchs/doc/DielectricStrength.htm for a chart. For air at STP it's about 3000 volts per millimeter In interpreting that chart, remember that standard atmospheric pressure is 760 torr, and at 2000 meters altitude (the notorious 6500 ft) the pressure is about 600 torr. Pressure and density aren't linearly related because of the temperature drop as you go up, but its a decent approximation for the first couple thousand meters or so. By the time you reach 300 torr, at about 7500 meters, the dielctric strength of air is degraded by about a factor of 2, and by 30,000 meters (10 torr) it's degraded by about 90%. We routinely fly our balloons above 38,000 meters. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Multimeter Altitude Limits
Hi Mike, i have taken my Fluke DMM up into the hills... No problems. The only altitude sensitive components might be the LCD and some DMM's have spark gaps which might short on AC prematurely at high elevation. i doubt there is any problem. i operate out of Cripple Creek frequently. Paul w0rw ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Multimeter Altitude Limits
Plasma displays have a 6500' limit. LCD displays shouldn't have the same limit, though I've seen specs on meters with LCD displays that say 6500'. So maybe it's not the display. Craig NZ0R -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Napier Sent: Thursday, August 03, 2006 11:23 AM To: elecraft@mailman.qth.net Subject: [Elecraft] Multimeter Altitude Limits While searching for a decent DMM to use during my K2 construction I noticed several of them have an altitude limit of 2000m (~6500 feet). Since I live at 7,600 feet and frequent altitudes at 10,000 while camping I am concerned about this limit. A call to the Extech Tech Support line yielded a service rep who was as mystified as myself as to this limit. Any expert opinions out there concerning this issue? Any DMM recommendations for a unit $60 to $100 or so? Mike K0MIS Cascade, CO ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Multimeter Altitude Limits
In a message dated 8/3/06 12:28:37 PM Eastern Daylight Time, [EMAIL PROTECTED] writes: Any expert opinions out there concerning this issue? (altitude) Cooling? 73 de Jim, N2EY ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Multimeter Altitude Limits
What's the upper voltage limit the DMM will handle? Resistors have a voltage rating as well as resistance and wattage (dissipation) ratings. We don't normally run into the voltage rating with leaded parts, especially with low-voltage solid state gear, but it's a very real concern as the voltage gets up there. That's why high voltage probes have big, long resistors or a number of resistors in series - shorter/smaller ones would arc over. In a DMM, the voltage divider that determines the voltage range is usually made in one piece, using tiny resistive elements on a substrate. Compared to normal resistors, each resistive element is tiny, and the voltage required to produce an arc drops dramatically as you go up in altitude. Radio equipment intended for use in an unpressurized aircraft or an unpressurized area in an aircraft is usually pressurized to avoid that corona discharges and arcing (as any tech will tell you who forgets to depressurize an aircraft radio before removing the cover bolts to service it. Me? Naw. The cover missed me by half an inch, at least...). If your DMM will measure a few hundred volts, I'd surmise arcing in the voltage divider is the limiting factor for altitude. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Multimeter Altitude Limits
In our high altitude ballooning program at LSU (120,000 feet) it's necessary to be very careful about sharp edges and corners in circuits of even modest voltages. Vacuum chamber testing is an essential part of the payload development. Our student payload had a Geiger-Muller tube, and that's a couple hundred volts, so they had to be sure to test in the chamber. Interestingly... 6500 ft is 1981 meters, so I speculate a conversation like.. Pointy Haired Boss: We need an altitude limit because of HV arcing, what do think it should be? Alice: Oh, couple thousand meters or so should be safe enough. Pointy Haired Boss: OK, tell marketing. Alice: Fine, but remember we're selling it in the USA. Pointy Haired Boss: Not to worry, ad copy writers will take care of conversion. I recall a wireless device whose range was specified on the package to be up to 328 feet. Amazing how they knew it would work at 327 but not at 329. Of course what was meant was that the range was about 100 meters. :^)) 73 Jim N5IB ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
